1st ANFEC Training workshop

On

Environmental Contaminant Analysis

18-20 December, 2012

at Royal University of Phnom Penh

Royal University of Phnom Penh

Organized by: Asian Network of Research on Food and Environment Contaminants (ANFEC)

Supported by: Royal University of Phnom Penh, Cambodia International Science Programme, Uppsala University, Sweden.

Analysis of Arsenic By Silver Diethyldithiocarbamate Method

Dr. Mohammad Arifur Rahman

Department of ChemistryUniversity of DhakaDhaka-1000Bangladeshrmarif@univdhaka.edu

Arsenic determination by the silver diethyldithiocarbamate method and the elimination of metal ion interferences: By Shingara S. Sandhu

Reprints from the collection of the university of Michigan Library

A rapid colorimetric method for measuring arsenic concentrations in groundwater

R.K. Dhara,b,c, , Y. Zhenga,b,c, J. Rubenstonec, A. van Geenc∗a School of Earth and Environmental Sciences, NSB D-216, Queens College, City University of NewYork,65-30 Kissena Building, Flushing, NY 11367, USAb Graduate School and University Center, City University of NewYork, NY, USAc Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USAReceived 5 May 2004; received in revised form 16 September 2004; accepted 16 September 2004

Spectrometric Method of Analysis

Arsine (AsH3) generation followed by complexation with silver –diehyldithiocarbamate

[Ag-SCSN (C2H5)2] solution: Arsenic reacts with a solution of Ag-DDTC, complex with

morpholine in chloroform to form soluble red complex, which has an absorption maximum

at 535 nm.

Trivalent arsenic reacts with silver-diehyldithiocarbamate [Ag-SCSN(C2H5)2] to form a

red color complex, which absorbs at 535 nm.

Ag-DDTC + AsH3 → As-DDTC (red color)

This is one of the standard and reliable method for arsenic determination in water at the

ppb (parts per billion), g/L, level.

5 valence As ion (As5+)+ (HCl, KI, SnCl2)→ 3 valence As ion (As3+)

By adding Zn to this solution, the arsenic is reduced further to arsenic hydride.

Preparation of Ag-DDTC Solution for Arsenic Adsorption

The solution was prepared by dissolving 0.75 g Ag-DDTC in a solution of 1 ml of

morpholine dissolved in 100 ml of chloroform. Then it was kept in a round bottom

quick fitted flask covering with aluminium foil and preserved at 4 degree in a

refrigerator.

Principle:

Inorganic arsenic is reduced to arsine by zinc in acid solution in a Gutzeit

generation (modified). The arsine is then passed through a scrubber

containing glass wool impregnated with lead acetate solution and into an

absorber tube containing Ag-DDTC.

Preparation of necessary Solution and Reagent

Preparation of Potassium Iodide Solution

15 g potassium Iodide (KI) was dissolved in 100 mL distilled de-ionized

water.

Preparation of Stannous Chloride 10%

10 g stannous chloride (SnCl2.2H2O) was dissolved in 100 mL distilled de-

ionized water.

Preparation of Stand Standard Curve for Arsenic Measurement:

Standard curve was prepared for total arsenic in concentration 5, 10, 15, 20 and 40 ppb.

Then the standard curve was prepared plotting the amount of arsenic (in ppb) along X axis and absorbance along Y-axis.

The arsenic content of water was then measured with the help of the curve.

Procedure

Treatment of Sample

50 mL sample was taken into a clean generator bottle (quick fitted 100 ml conical flask) adding successively, 5 mL 1:1 HCl, 5 mL KI (15%) solution and 8 drops SnCl2 reagent.

Preparation of Scrubber and Absorber

Cotton was impregnated in the scrubber with lead acetate solution and 4 mL Ag-DDTC reagent was taken with a pipette in absorber tube.

Arsenic Generation and Measurement

Adding 1g Zn-dust to generator, it was connected with scrubber absorber immediately.

All connection must be fitted tightly. Allowing 30 min, for complete evolution of arsine and pouring solution absorber into a 1 cm cell, the absorbance was measured at 540 nm, using the reagent blank as the reference.